The techniques of channel separation, range gate, variable gain of photomultiplier tube and cross polarization are analyzed and combined to improve the dynamic range compression of the laser echo signal in airborne laser bathymetry. The corresponding device with variable gain is developed, and implemented in experiments in tank and sea in situ. Results show that the combined technique compresses the dynamic range of submarine signal effectively and meets the demand of shallow sea dynamic range for the airborne laser bathymetry. The technique of cross polarization does not improve the effect of measuring signal compression remarkably, and the influence of after pulse effect of photomultiplier tube on depth measurement is also reported. Valuable reference for further study on dynamic range compression is presented.